1. Field of the Invention
The present invention relates to the preparation of .beta.,.gamma.-unsaturated acids, and, more especially, to the preparation of .beta.,.gamma.-unsaturated acids by the carbonylation of allyl alcohols.
2. Description of the Prior Art
U.S Pat. No. 4,189,608 describes a process for preparing 3-butenoic acid by contacting allyl alcohol with carbon monoxide in the presence of a palladium chloride-based catalyst at a temperature ranging from 50.degree. to 300.degree. C. under high pressure, the reaction being carried out in a substantially anhydrous C.sub.2 -C.sub.10 carboxylic acid as a liquid solvent.
In point of fact, the carboxylic acid is liable to react with the alcohol to produce an allyl carboxylate, which would become the reactant for the palladium-catalyzed carbonylation.
Moreover, the catalytic activity remains low, as evidenced by the relatively lengthy reaction times.
U.S. Pat. No. 4,025,547 describes the carbonylation of primary allyl alcohols into esters of the allyl vinylacetate type, in the presence of a homogeneous catalytic system containing three components:
(i) a palladium halide; with PA1 (ii) one or more donor ligands of Group VB; and PA1 (iii) a cocatalyst which is a halide of a Group IVB metal.
A typical example of these catalytic compositions is PdCl.sub.2 (P(C.sub.6 H.sub.5).sub.3).sub.2.SnCl.sub.2.
Triphenylphosphine, as well as tin dichloride, may be introduced, in excess.
In this process, an allyl ester is formed instead of an acid; the allyl alcohol serves both as a substrate which is carbonylated under the reaction conditions and as an esterification reagent. Moreover, the pressures employed are very high.
German Offenlegungsschrift 3,345,375 describes a process for the carbonylation of secondary or tertiary allyl alkanols in the presence of palladium halides complexed with a phosphine, where appropriate in excess, at 50.degree.-150.degree. C. under high pressure.
While the selectivity of the reaction appears to be appreciable, the activity of the catalytic system remains low, as evidenced both by the lengthy reaction times and the very high pressures which are employed in this process.